1. Field of the Invention
The present invention is directed to a chalk line retraction device which employs a spirally wound band spring coupled to a chalk line reel at a mechanical advantage.
2. Description of the Prior Art
Chalk lines are widely used during building construction for marking lines on floors, walls and the like where cuts are to be made or where cabinets, shelves and other built-in furnishings are to be installed. A chalk line is wound on a reel or spool and coated with dry chalk. The free end of the chalk line is held at a predetermined location and the chalk line is stretched to the opposite end of a line to be marked. The ends of the chalk line are placed against the surface to be marked and the length of the chalk line therebetween is stretched taut. The center of the chalk line is then drawn outwardly from that surface and released. The resiliency of the chalk line causes the line to rebound against the surface to be marked, thereby causing a linear chalk marking to be formed upon a wall or floor. Markings of this type facilitate the making of straight cuts and the installation of lengthy furnishings.
Various different chalk line retraction device have been constructed to aid in winding a chalk line on a reel or drum. One prior automated retractable chalk line assembly is described in U.S. Pat. No. 4,565,011. This device employs a chalk line mounted on a spool which is coupled through gearing to a wire, coil spring. However, the device of that assembly is capable of automatically retracting a chalk line of only a very short length, since the ends of the coil spring can only undergo very limited angular rotational displacement relative to each other.
In the system of U.S. Pat. No. 4,565,011 a long length of chalk line will be only partially retracted before the spring is totally relaxed and must be retensioned to aid in retracting any more of the chalk line. Thus, to fully retract a long length of chalk line it is necessary to repeatedly rewind the spring with the chalk line locked, then release the chalk line lock so that an additional portion of the unwound chalk line can be retrieved. Such an arrangement is quite inefficient, since it requires the user to manually retension the spring in a repeated series of steps to fully retract a long length of chalk line.